1. Field of the Invention
The invention pertains to a method and an apparatus for inspecting for bad wiring and pixels in a flat display device by using a magnetic sensor.
2. Description of the Related Art
The importance of a display apparatus as a visual information transfer medium has recently enlarged. Widely used conventional cathode ray tubes have undesirable weight and large volume. There has therefore been developed various types of flat display apparatuses capable of overcoming the disadvantages of cathode ray tubes.
These flat display devices include a liquid crystal display (LCD), a field emission display (FED), a plasma display panel (PDP) and an electroluminescence display (EL). Most of these displays are available in the marketplace.
The liquid crystal display readily adapts to miniaturization and has enhanced productivity. Thus, LCDs are rapidly replacing the cathode ray tube in many applications.
Specifically, an active matrix type liquid crystal display apparatus that drives a liquid crystal cell by using a thin film transistor (hereinafter referred to as “TFT”) has an advantage of excellent picture quality combined with low power consumption. This technology has rapidly developed to large volume production of high definition displays due to recent research and the application of productivity technology.
The process for fabricating an active matrix type display device is divided into substrate cleaning, substrate patterning, alignment forming/rubbing, substrate assembling/liquid crystal material injecting, mounting, inspecting and repairing.
Impurities on a substrate surface of the liquid crystal display device are removed by a detergent during the substrate cleaning process.
The substrate patterning process includes patterning of an upper substrate, i.e., a color filter substrate, and patterning of a lower substrate, i.e., a TFT array substrate. There are formed a color filter, a common electrode and a black matrix on the upper substrate. Signal wires such as a data line and a gate line are formed on the lower substrate, and the TFT is formed at an intersection of the data line and the gate line. A pixel electrode is formed in a pixel region between the gate line and the data line connected to a source electrode of the TFT.
An alignment film is applied to each of the upper substrate and the lower substrate in the alignment film forming/rubbing process, and the alignment film is rubbed by a rubbing material.
In the substrate assembling/the liquid crystal injection process, both of the upper substrate and the lower substrate are bonded together by a sealant, and the liquid crystal material and a spacer are injected through a liquid crystal injection hole. The liquid crystal injection hole is then sealed.
The mounting process of the liquid crystal panel uses a tape carrier package (hereinafter referred to as “TCP”) having integrated circuits mounted thereon, such as a gate drive integrated circuit and a data drive integrated circuit is connected to a pad part on the substrate. Such drive integrated circuits maybe directly mounted on the substrate by using a chip on glass (herein after referred to as “COG”) method other than TAB (Tape Automated Bonding) using the TCP described above.
The inspection process includes a first electrical inspection being performed after forming a variety of signal wires and the pixel electrode, and an electrical inspection and a visual inspection being performed after the substrate assembly/liquid crystal injection process. Specifically, the electrical inspection of the signal wires and the pixel electrode of the lower substrate, followed by substrate assembly, may reduce the defect ratio and the amount of waste matter. A bad substrate may also be reparable at an early stage, and thus its importance gradually increases.
The repairing process performs a restoration of a repairable substrate discovered by the inspecting process. However, in the inspecting process, defective substrates that are beyond repair are discarded.
The electrical inspection being performed before substrate assembling frequently employs a method using an apparatus shown in FIG. 1.
Referring to FIG. 1, the electrical inspection process is performed as follows: a separate modulator 10 has a designated gap over a test substrate 11. Applying a test voltage (Vtest) to the modulator, while maintaining the gap, and detecting light reflected from the modulator 10 determines any electrical defects of the signal wires 17 and 18.
In the modulator 10, a polymer-dispersed liquid crystal (hereinafter referred to as “PDLC”) is located between an upper transparent substrate 12, having a common electrode 13 formed thereon, and a lower transparent substrate 15. In the modulator 10, a reflection sheet 16 is set up toward a rear surface of the lower transparent substrate 15. The modulator 10 has an air nozzle and a vacuum nozzle for an auto-gapping, which maintains the designated interval from the substrate 11 to be tested.
Above the modulator, a lens 21 light-gathers the light from a light source (not shown) into the modulator 10, and the lens 21 additionally transmits the light 22 reflected from the modulator 10.
The test substrate 11 includes a lower substrate having the TFT 19 thereon. Signal wires 17 and 18 and the pixel electrode 20 are formed in an active matrix type liquid crystal display device.
The electrical inspection begins by loading the test substrate 11 below the modulator 10, and the modulator descends while performing the auto-gapping. While maintaining the gap between the modulator 10 and the test substrate 11 at a predetermined effective gap, the light is radiates from the light source (not shown), and the light focuses on the modulator 10 by the light-gathering lens and simultaneously a test voltage (Vtest) is applied to the common electrode 13. Test data supplied from a driving circuit is applied to the data wires 17, and a test scan signal is applied to the gate wires 18. Then, an effective electric field is applied to the PDLC 14 between the common electrode 13 of the modulator 10 and the pixel electrode 20 being tested.
When the electric field is not applied, the PDLC 14 causes the light to scatter. When the effective electric field (E) is applied, the liquid crystal orients according to the direction of the effective electric field (E) and causes the light to transmit. Accordingly, in the electrical inspection process, when the voltage is normally applied to the pixel electrode 20, the corresponding liquid crystal layer of the PDLC 14 causes the light 22 to transmit. When the voltage is not applied to the pixel electrode 20, the liquid crystal layer of the PDLC 14 causes the light to be scattered in that part.
While the light 22 transmitting the liquid crystal layer of the PDLC 14 is reflected by the reflection sheet 16 and then is reverse directed to the light path, the light 22 scattered in the liquid crystal layer of the PDLC 14 is nearly vanishes and is not nearly incident to the reflection sheet 16. The light reflected in the modulator 10 is received to a charge-coupled device (CCD) (not shown) via the lens 21 and then is converted in an electrical signal. Then, the converted signal is transferred to a display (not shown) via a signal processing circuit. A testing inspector monitors an image or data displayed in the display to determine whether defects are present. The test inspector secondarily performs a close inspection of any doubtful signal wires 17 and 18.
The modulator 10 has the advantages of exactness and reliability for inspecting for defects pixel-by-pixel, but these advantages come at a high cost. Further, since the inspection region is narrow as compared to the total area of the substrate 11, the modulator 10 must repeat the inspection process by moving in a designated length in the vertical or the horizontal direction and then temporarily stopping for auto-gapping. Thus, the inspection time is disadvantageously extended. Further, the exactness of the modulator 10 with respect to the highly fine detail of the flat display device is lower than desired.
For example, FIG. 2 shows a portion of the first column and the second row of the pixel electrode PIX (1,2) among the pixel electrodes PIX (1,1) to PIX (2,3) formed in the pixel region between the data wires 32a, 32b and 32c, and the gate wires 31a and 31b are lost due to bad patterning. When a test scan voltage is applied to the gate wire 31a and simultaneously a test data voltage is applied to the data wire 32b, since the test data voltage is supplied to the first column and the second row of the pixel electrode PIX (1,2) via the TFT (not shown), an electric field is generated between the pixel electrode PIX (1,2) and the common electrode 13 of the modulator 10 as in normal pixel. As a result, since reflecting light is collected by a charge-coupled device via the modulator 10 in the pixel corresponding to the first column and second row of the pixel electrode PIX (1,2), the pixel is determined to be normal.